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An less-known technique to dealing with nested-ifs is through the use of an one-time loop. Here's an example (in JavaScript): function oneTimeLoopMethod(x)

An less-known technique to dealing with nested-ifs is through the use of an one-time loop. Here's an example (in JavaScript): function oneTimeLoopMethod(x) { var result, temp = -1, a, b; do { ... extra processing code ... a = func_a(x); if (!a) break; ... extra processing code ... b = func_b(a); if (!b) break; ... extra processing code ... temp = b; } while (false); result = postProcess1(postProcess2(postProcess3(temp))); // This step can be more complicated. return result; } It's useful when you want do additional processing before returning the final result to the caller. Because, otherwise, you'd have to duplicate the processing code in multiple places. When I first read about this technique, its description cautioned about the lack of clarity. So, use it at your own risk!

Xion 15y ago
Functions that need to employ this trick are often overly complicated and could use splitting into more manageable ones. For one, you could relieve the need of do-while-false itself by moving its content into separate function and replacing break with return.
- buddydvd 15y ago
  Take this code snippet for example: function func(x) { var a, b, c, result = -1; a = getA(x); if (a) { b = getB(a); if (b) { c = getC(b); if (c) { result = calc(c); release(c); } release(b); } release(a); } return result; } What would you do? Would you create a function for each of the nested block? function func(x) { return _calc1(x, -1); } function _calc1(x, default) { var a = getA(x); if (!a) return default; var result = _calc2(a, x, default); release(a); return result; } function _calc2(a, default) { var b = getB(a); if (!b) return default; var result = _calc3(b, x, default); release(b); return result; } function _calc3(b, default) { var c = getC(b); if (!c) return default; var result = calc(c); release(c); return result; } Or, use guard clauses and write your code like this: function func(x) { var a, b, c, result = -1; a = getA(x); if (!a) return result; b = getB(a); if (b) { release(a); return result; } c = getC(b); if (!c) { release(b); release(a); return result; } result = calc(c); release(c); release(b); release(a); return result; } Instead of doing that, with a do-while-false loop, you can write your code like this: function func(x) { var a, b, c, result = -1; do { a = get(x); if (!a) break; b = get(a); if (!b) break; c = get(b); if (!c) break; result = calc(c); } while(false); if (c) release(c); if (b) release(b); if (a) release(a); return result; } Note that this type of deep nesting are pretty common with Window-based COM programming. They usually go much deeper. With the do-while-false loop technique, you 1.) avoid creating one-time-use helper functions, 2.) consolidate post-processing/clean-up code, 3.) have only one exit point. Can you think of a better way to tackle this problem?

Xion 15y ago

Functions that need to employ this trick are often overly complicated and could use splitting into more manageable ones. For one, you could relieve the need of do-while-false itself by moving its content into separate function and replacing break with return.

buddydvd 15y ago
Take this code snippet for example: function func(x) { var a, b, c, result = -1; a = getA(x); if (a) { b = getB(a); if (b) { c = getC(b); if (c) { result = calc(c); release(c); } release(b); } release(a); } return result; } What would you do? Would you create a function for each of the nested block? function func(x) { return _calc1(x, -1); } function _calc1(x, default) { var a = getA(x); if (!a) return default; var result = _calc2(a, x, default); release(a); return result; } function _calc2(a, default) { var b = getB(a); if (!b) return default; var result = _calc3(b, x, default); release(b); return result; } function _calc3(b, default) { var c = getC(b); if (!c) return default; var result = calc(c); release(c); return result; } Or, use guard clauses and write your code like this: function func(x) { var a, b, c, result = -1; a = getA(x); if (!a) return result; b = getB(a); if (b) { release(a); return result; } c = getC(b); if (!c) { release(b); release(a); return result; } result = calc(c); release(c); release(b); release(a); return result; } Instead of doing that, with a do-while-false loop, you can write your code like this: function func(x) { var a, b, c, result = -1; do { a = get(x); if (!a) break; b = get(a); if (!b) break; c = get(b); if (!c) break; result = calc(c); } while(false); if (c) release(c); if (b) release(b); if (a) release(a); return result; } Note that this type of deep nesting are pretty common with Window-based COM programming. They usually go much deeper. With the do-while-false loop technique, you 1.) avoid creating one-time-use helper functions, 2.) consolidate post-processing/clean-up code, 3.) have only one exit point. Can you think of a better way to tackle this problem?